The overall objective of this research program is to localize and identify at the electron microscopic level certain carbohydrate-containing macromolecules on developing photoreceptor synaptic membranes in the chick retina. Cell surface carbohydrates on developing synaptic membranes have been visualized by the use of lectin-peroxidase conjugates at various stages of photoreceptor synaptogenesis. In addition, a further characterization of the chemical nature of developing synaptic membrane carbohydrates has been obtained by testing the effects of proteolytic and glycolytic digestion on lectin staining. Furthermore, other developing visual systems have been used to characterize various aspects of synapse formation. This past year we have extended our investigations of synaptogenesis to include not only structural but functional aspects of the mature photoreceptor synapse and its membrane compartments during light and dark adaptation. This work should enable us to better evaluate our ultrastructural, freeze-fracture and lectin cytochemical data obtained from our studies on synaptogenesis, in terms of the functional implications for the developing and mature synapse.